The present invention relates generally to oscillators and in particular the present invention relates to variable rate oscillators having temperature variable frequencies.
It is sometime desirable to know the internal temperature of integrated circuits. For example, dynamic random access memory (DRAM) devices require periodic refresh cycles in order to maintain the integrity of the data stored in the memory. The temperature of the memory device affects the frequency at which the memory device needs to be refreshed. As the device heats up, the cells lose their ability to hold a charge due to current leakage. Therefore, the warmer the device the more often it has to be refreshed.
Designers typically take into account the worst case requirement for refreshing a DRAM and design the memory to refresh at a fixed rate consistent with the maximum operating temperature of the part. However, the faster refresh rate is not required when the device is operating at a cooler temperature, thus wasting power. It would therefore be beneficial to be able to determine the memory device's internal temperature in order to adjust the refresh rate in response to changing temperature. In a battery powered electronic device, a smaller power requirement could translate into either a smaller battery or longer battery life.
Additionally, some battery powered electronic devices use ambient and device temperature readings to monitor system heating during battery charging. Such devices typically require at least one external temperature sensor that adds to the weight and expense of the electronic device. In a market where profit margins are small and size/weight might determine marketing advantage, a less expensive and smaller device is more desirable.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a temperature sensing device that can be used by both an integrated circuit and any peripheral circuitry.